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Refactor the sqlite3_randomness() implementation for improved performance.

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FossilOrigin-Name: 4144dffb57b5ed791d7a6d2f26fab5e7dc77fbd1
This commit is contained in:
drh 2013-08-21 22:09:25 +00:00
parent b49bc86a1a
commit cf5ff12105
3 changed files with 21 additions and 44 deletions
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12
manifest
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@ -1,5 +1,5 @@
C Simplification\sto\sthe\sStrAccum\sobject\sand\sthe\ssqlite3StrAccumAppend()\nmethod\sthat\salso\sresults\sin\sslightly\sbetter\sperformance.
D 2013-08-21T21:12:10.959
C Refactor\sthe\ssqlite3_randomness()\simplementation\sfor\simproved\sperformance.
D 2013-08-21T22:09:25.294
F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
F Makefile.in 5e41da95d92656a5004b03d3576e8b226858a28e
F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@ -213,7 +213,7 @@ F src/pcache1.c a467393909a4ed7ca9de066d85ba5c5b04a5be63
F src/pragma.c 1d96ba749253b49bc229c6294f9c2e5ef3dca85c
F src/prepare.c fa6988589f39af8504a61731614cd4f6ae71554f
F src/printf.c da9119eb31a187a4b99f60aa4a225141c0ebb74b
F src/random.c cd4a67b3953b88019f8cd4ccd81394a8ddfaba50
F src/random.c 0b2dbc37fdfbfa6bd455b091dfcef5bdb32dba68
F src/resolve.c 9d53899cc6e1f4ec0b4632d07e97d57827bf63b9
F src/rowset.c 64655f1a627c9c212d9ab497899e7424a34222e0
F src/select.c 8b148eb851f384412aea57091659d14b369918ca
@ -1105,7 +1105,7 @@ F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
F tool/wherecosttest.c f407dc4c79786982a475261866a161cd007947ae
F tool/win/sqlite.vsix 97894c2790eda7b5bce3cc79cb2a8ec2fde9b3ac
P ef2a6a37366f91889dc2f1ba9cb6d1257d9b05db
R b5f522403c7336cdf922a181f76ebfed
P 700dbbea8647e0fdaee6d0aba3d3dd8ebfbac04a
R bace2fbe40d117379ef5fcee60c09ed4
U drh
Z 3ab1c9a1ca4e97a25908645404ada3f7
Z a22b19ec66f802a5577e622202a99c6b

2
manifest.uuid
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@ -1 +1 @@
700dbbea8647e0fdaee6d0aba3d3dd8ebfbac04a
4144dffb57b5ed791d7a6d2f26fab5e7dc77fbd1

51
src/random.c
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@ -28,24 +28,11 @@ static SQLITE_WSD struct sqlite3PrngType {
} sqlite3Prng;
/*
** Get a single 8-bit random value from the RC4 PRNG. The Mutex
** must be held while executing this routine.
**
** Why not just use a library random generator like lrand48() for this?
** Because the OP_NewRowid opcode in the VDBE depends on having a very
** good source of random numbers. The lrand48() library function may
** well be good enough. But maybe not. Or maybe lrand48() has some
** subtle problems on some systems that could cause problems. It is hard
** to know. To minimize the risk of problems due to bad lrand48()
** implementations, SQLite uses this random number generator based
** on RC4, which we know works very well.
**
** (Later): Actually, OP_NewRowid does not depend on a good source of
** randomness any more. But we will leave this code in all the same.
** Return N random bytes.
*/
static u8 randomByte(void){
void sqlite3_randomness(int N, void *pBuf){
unsigned char t;
unsigned char *zBuf = pBuf;
/* The "wsdPrng" macro will resolve to the pseudo-random number generator
** state vector. If writable static data is unsupported on the target,
@ -60,6 +47,10 @@ static u8 randomByte(void){
# define wsdPrng sqlite3Prng
#endif
#if SQLITE_THREADSAFE
sqlite3_mutex *mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG);
sqlite3_mutex_enter(mutex);
#endif
/* Initialize the state of the random number generator once,
** the first time this routine is called. The seed value does
@ -88,28 +79,14 @@ static u8 randomByte(void){
wsdPrng.isInit = 1;
}
/* Generate and return single random byte
*/
wsdPrng.i++;
t = wsdPrng.s[wsdPrng.i];
wsdPrng.j += t;
wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j];
wsdPrng.s[wsdPrng.j] = t;
t += wsdPrng.s[wsdPrng.i];
return wsdPrng.s[t];
}
/*
** Return N random bytes.
*/
void sqlite3_randomness(int N, void *pBuf){
unsigned char *zBuf = pBuf;
#if SQLITE_THREADSAFE
sqlite3_mutex *mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG);
#endif
sqlite3_mutex_enter(mutex);
while( N-- ){
*(zBuf++) = randomByte();
wsdPrng.i++;
t = wsdPrng.s[wsdPrng.i];
wsdPrng.j += t;
wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j];
wsdPrng.s[wsdPrng.j] = t;
t += wsdPrng.s[wsdPrng.i];
*(zBuf++) = wsdPrng.s[t];
}
sqlite3_mutex_leave(mutex);
}